I created this PF haul truck to keep my modified 8043 excavator busy and out of trouble. Last week, the darned thing turned our shower floor into an engineered landfill of used cat litter while we were at work!

Time-outs no longer have any effect -- it just digs up its room. Clearly what this excavator needs is a job.

The sequence below shows the haul truck keeping the excavator occupied at a nearby pinto bean mine. (Really? You didn't know that pinto beans are mined?)

The haul truck loves spilling the beans as much as the excavator tries not to. The excavator can't bear to watch.

I hire women to drive all of my heavy equipment. They show up on time, put safety first, and don't cut corners. Turns out that real haul trucks are often driven by women for exactly the same reasons.

Introduction

Actually, the real inspiration for this haul truck (short for ultra-class rigid-frame off-highway dump truck, typically a mining truck) came from at least 2 sources.

The 1st was my heavily modified 8043 motorized excavator (above) -- hands down, my favorite set of all time. I built this 8043 directly to the superb 8043 modifications engineered by Jurgen Krooshoop, adding a few mods of my own along the way. The resulting functionality was so realistic and so entertaining that I had no choice but to build a dump truck to go with it.

Shortly thereafter, on a road trip through the Canadian Rockies, we stumbled onto the 2nd inspiration: The original haul truck -- the Terex 33-19 "Titan", now on display in a park in Sparwood, BC.

[terex]

I'd seen pictures of these monsters, but after standing next to and under (yes, under) one, I knew that my excavator would soon have its truck.

Online haul truck research eventually led to a detailed Liebherr T284C product brochure with 3-view line drawings showing all the necessary dimensions.

That info and online images of a striking white T284C clinched the T284C as the basis for my haul truck. (Not that it mattered much -- haul trucks all look pretty much alike, and a high-fidelity model of a particular truck wasn't the goal.) The color, however, would have to be yellow to keep the cost down.

For the chassis, I chose a 4x4 Crawler (9398) chassis I'd built and set aside several months earlier for lack of interest in the bodywork -- not because the 9398 chassis is a good match for a haul truck (it isn't), but because it was paid for and needed new clothes.

The T284C chassis differs from the 9398's in important ways:

On the T284C, only the front wheels are steered, and only the rear wheels are driven; hence, it's a 4x2x2, not a 4x4x4.

The T284C has independent double A-arm front suspension and a hard-tail rear axle.

The T284C has dual rear wheels.

Worst of all from a visual standpoint, the 9398 chassis is way too narrow. The MOC's overall width should be 40% greater to match its overall length and height.

Aside from these discrepancies, my haul truck does reasonable justice to the T284C.

The model was completed just in time for a LEGOŽ show in Loveland, CO in November, 2013. It was quite a hit with the boys and more than few girls, and many of them got to drive it. 1

At one point, I noticed a man and woman discussing the truck at length. Turns out that he'd driven the Caterpillar equivalent, the 797F, for several years. I must have picked his brain for a good 20 minutes. 2

When asked what it was like to drive one, he said, astoundingly, that aside from the long climb to the cab, it was pretty much like driving his car!

"But that truck weighs over a million pounds!" I protested, but he wasn't kidding. "So what kind of car do you drive?" I asked, imagining some kind of monster truck, or at least a jacked-up dually.

"A Ford Escort."

Why haul trucks?

Haul trucks exist because they move large volumes of bulk materials more quickly and efficiently than a herd of smaller trucks with the same total capacity when all costs are considered.

The T284C specs below give a feel for what it takes to achieve this economy of scale:

I consider it a miracle that, after all the fiddling it took to get a 42° dump angle (see below), the top edge of the dump body (which could only be made with 18° slope bricks) came out almost exactly horizontal -- as it must be to reduce the likelihood of bucket strikes during loading.

The next 4 images underscore one of the disadvantages of using the narrow 9398 chassis in an inherently top-heavy haul truck: The 4-wheel steering and pendular suspension together cause the chassis -- and the dump body with it -- to list to one side when the wheels are turned.

Dump body lowered; 4-wheel steering: Among other things, the next 5 images show details of the underside of the dump body, the dump body hinge, the rear pendular axle and suspension, and the wheel lock provided by the PF stepper motor used for steering.

The stepper motor's almost twice as expensive as the L motor next in line, but sure it takes a lot of the sting out of engineering LEGOŽ steering mechanisms.

Footprint: The next photo gives an idea of the MOC's overall footprint. The light-colored floor tiles were 305 mm (12 in) squares before corner cuts.

Dump body raised: The next 4 images show the MOC from various angles with the dump body raised. The 4 ball joints attaching the protective canopy to the dump body hold their angles fairly well, but do droop now and then. Achieving a dump angle of 42° took quite a bit of doing, as detailed below.

Map view of deck features: From top (driver's left) to bottom, gondola-like cab, AAA battery box, yellow control cabinet, and dual PF IR receivers. One of the wires leads to the steering stepper motor just aft of the battery box.

The yellow boxes attached to both sides of the gray chassis behind the deck are fuel tanks. At far right in the image are the black stairs from the front bumper to the deck. The latter sits 5.2 m (17.2 ft) above the ground on the T284C.

A look at the undercarriage.

Details

More detailed commentary follows the pictures below. NB: Hereafter, I'll be using "right" and "left" as the driver sees them, not as they appear in the images.

It's change of shift. The minifig on deck has just climbed the steps in front of the massive radiator grille and is now headed for the cab on the left side of the deck.

Several small cabinets occupy the right side of T284C's deck, about where the oversized twin PF IR receivers sit. A round convex side mirror sits at the right front corner of the deck. A larger flat rectangular side mirror rises from the left edge.

Haul trucks like the T284C are like deisel-electric locomotives: Their enormous diesel engines are there only to run the generators powering their electric propulsion motors and other electrical needs.

One has to question the wisdom of driving a truck that requires so many fire extinguishers. The T284C sports 7 of them in the locations shown. Why?

The former haul truck driver I met in Loveland told me that the big yellow control cabinet at the back of the deck tends to go up in flames now and then. When it does, the extinguishers are there only to clear an escape route, not to fight the fire per se. He's seen one of these cabinets burn a haul truck to the ground.

To increase the odds of escape, real T284Cs have 2 additional, very steep escape ladders, one on each side of the radiator. I omitted these, as modeling the stairs in front of the radiator was hard enough.

Turns out that the yellow control cabinet houses two system hubs side by side -- one for the high-amperage electrical system, and the other for the high-pressure forced lubrication system.

One also has to question the wisdom of running huge electric currents right next to huge flows of lubricating oil in the same cabinet. There must be some compelling reason for doing so, because Liebherr and Caterpillar both put control cabinets like this on haul truck decks.

Close-up of the right convex side mirror, IR receivers, yellow control cabinet, and some fire extinguishers.

This MOC needs 3 IR receiver connections -- 1 to control both propulsion L motors simultaneously, 1 to control the steering stepper motor, and 1 to control the dump body M motor.

Just to add to the excitement, I put the PF AAA battery box powering the IR receivers right behind the fire-prone yellow control cabinet.

The black box below the front edge of the deck here looks like a giant covered dual headlight, but it's actually an engine air intake. To get a 6L railing of sorts, I had to cut the bottom off a 4-bar grate and mount it on the 6L base shown.

Left side view of the deck, cab, and middle part of the chassis. The yellow box with a trapezoidal face attached to the chassis is the left fuel tank.

An oblique view of the left side of the truck from behind.

Cab: Shot of the cab from above and behind. Pulling out the 8L pin with stop at bottom center releases the left side of the battery holder. There's a corresponding pin on the right.

OSHA would have a fit over this topless cab, but the driver prefers convertibles.

Cab interior from above with flat side mirror to the left.

Why this truck has radar, I have no idea.

Dump body actuators: Large linear actuators driven by an M motor in the undercarriage raise and lower the dump body.

Gear trains for the dump body linear actuators yield a final reduction of 9:1. The driving M motor at center hides the steering stepper motor directly above it. Owners of the 4x4 Crawler set (9398) will recognize the steered portal axles front and rear.

Close-up of the left dump body actuator gear train.

Alert system: When the dump body lifts off the chassis, it releases the alert system lever seen here above and behind the left fuel tank.

Left fuel tank removed to reveal the Rube Goldberg-like linkage needed to convert the upward motion of the alert system lever into a press-and-hold of the klaxon brick button. (The button's hidden here, but the klaxon's orange circuit board can be seen through its transparent case.)

Concocting a reliable press-and-hold linkage in the very limited space available with only a few free pin holes turned out to be one of harder parts of this build.

As the dump body approaches the chassis, it depresses the alert system lever, causing the linkage to release the klaxon brick button. This sounds the klaxon again.

Dump angle: Getting as close as possible to the T284C's impressive 49° dump angle (between bed and the horizontal at full tilt) proved to be one of this build's greatest challenges. It was certainly the most aggravating.

Chassis differences precluded use of the actual geometry shown in the T284C brochure. There were only a few fixed parameters: (i) Location of the pivoting linear actuator (LA) attachments to the chassis, fixed by various 9398 chassis restrictions and my dump body actuator gear train design; (ii) height of the cab and its location along the chassis, fixed by a determination to scale these things properly; (iii) contact point on the rear end of the chassis -- the ultimate limit on dump angle; and (iv) fully extended and retracted LA lengths, fixed of course by LEGOŽ.

That left 5 parameters to be determined: (i) Location of the LA attachments along the dump body, (ii, iii) locations of the dump body hinge attachment along the dump body and chassis, and (iv, v) hinge arm lengths separating the dump body and chassis from the actual hinge axis. Pin holes that were off-limits for various reasons narrowed some of the free parameter choices, but not nearly enough.

The problem can't be solved geometrically, as it amounts to finding the limits of an interior angle of an underdetermined irregular pentagon when the side corresponding to an LA takes on its maximum and minimum lengths. In the end, it took a lot of tedious trial and error and luck to pull off a 42° dump angle.

Suspension issues: The dump angle solution meant that the rear shocks would have to be relocated. What I really needed was 2 pairs of rear shocks -- one to spring vertical pendular axle travel, and the other to further reduce chassis roll.

Unfortunately, creating effective attachment points for the 1st, more important pair without messing up my hard-won dump angle proved very difficult, and there simply weren't any effective attachment points for the desired 2nd pair.

A pendular suspension is probably the worst possible choice for a top-heavy haul truck. Together, the 9398 pendular suspension and 4-wheel steering are a recipe for excessive chassis roll. This haul truck never rolled over, but it often looked on the verge when heavily loaded.

I got rid of most of the roll by supplementing the front and rear shocks with paired 8L torsion bars linking the chassis mid-section to the front and rear pendular axle assemblies. These torsion bars flank the front and rear propulsion motors inboard of the upper chassis rails.

You can see the forward ends of the rear torsion bars in this photo just below and forward of the dump body hinge, but they're better seen in the photo before last.

Specifications

Overall dimensions:

495 x 216 x 252 mm (LxWxH) including front stairway

Overall weight:

2.65 kg empty

Construction:

Studded exterior and dump body on a modified 9398 studless chassis

Basis:

Liebherr T284C, but only loosely

Scale:

1:32 in length and height

Platform:

4x4x4 (2 axles)

Propulsion:

Simultaneously driven front and rear L motors

Dump body movers:

2 large linear actuators

Dump body capacity:

At least 2 kg

Dump angle:

42°

Alert system:

Dump body-activated klaxon brick

Roll stabiliztion:

Paired front and rear torsion bars

Fire extinguishers:

7

Motors:

4 in all -- 1 L for each axle, 1 PF stepper for steering, 1 M for dump body

Lights:

None

IR receiver connections:

3 in all -- 1 for both propulsion motors, 1 for steering motor, and 1 for dump body motor

1 For most of the boys, the first impulse was to go straight to bumper cars without even knowing how to drive the haul truck. The girls, on the other hand, would take a minute to master the controls before setting out on an imaginary trip to the mountains or the beach or the park with a friend.

2 Liebherr and Caterpillar both claim to make the highest-capacity truck in the world, and this has apparently been going on for years. Their current contenders are the T284C and the 797F, respectively.

Quoting Scott Bertaut
This thing is a beast! Nice job on making it look good and be functional, sounds like the people at the local LEGO con had fun with it too. Someday I hope to build some motorized construction trucks myself (probably smaller road fairing ones) but for now the citizens of Buildington have to rely on the folks at Rokenbok for their construction needs.

Thanks, Scott! I'd like to rebuild this one to proper width with a less tippy suspension, but it's still fun the way it is.

This thing is a beast! Nice job on making it look good and be functional, sounds like the people at the local LEGO con had fun with it too. Someday I hope to build some motorized construction trucks myself (probably smaller road fairing ones) but for now the citizens of Buildington have to rely on the folks at Rokenbok for their construction needs.